There are numerous methods for patterning metals on surfaces, many of which are widely practiced commercially, including for example photolithography with etching or with plating, inkjet printing, screen-printing, and laser patterning. At the same time, there are many other unique methods that to date have failed to displace the incumbent processes commercially, for example due to lack of a true advantage or due to significant technical barriers to implementation. Significant technical barriers have impeded the commercialization of microcontact printing in the etch-patterning of metals.
Microcontact printing is the stamping or rotary printing of self-assembled monolayer (SAM) patterns on substrate surfaces. The approach exhibits several technologically important features, including the ability to be carried out for very fine scale patterns (e.g., feature size of one tenth of a micrometer) and with the extension of the patterned monolayer to the patterning of metals, ceramics, and polymers. Notwithstanding these features, the method has been revealed through extensive research to pose significant challenges related to pattern geometry flexibility and to scale-up. By pattern geometry flexibility, what is meant is the ability to apply a method of patterning to a wide range of pattern geometries. For example, in the art it is known that microcontact printing patterns with widely spaced features leads to stamp deformation, including roof collapse, which leads to unacceptable pattern distortion and artifacts.
These issues have led to the engineering of composite stamps with complicated constructions, usually comprising very stiff or very thin layers of the elastomer stamp material, or sometimes including mounting of the stamp on supports or backplanes with specified properties. In other approaches, stamps with significant relief have been proposed, leading to challenges in mastering and printing. Often, the material changes or stamp construction or support measures lead to challenges in generating an inked stamp that can be used to print patterns efficiently, for example with high throughput and at competitive cost. Thus, in order to avoid the negative ramifications and complications of extensive stamp material substitutions or multilayer stamp construction, there is a need in the art to define pattern geometries that are more compatible with standard stamp materials and low levels of stamp relief.
As another example, in the art it is known that kinetic aspects of the process can substantially constrain the range of SAM pattern geometries that can be microcontact printed effectively and efficiently. The kinetic phenomena that govern successful microcontact printing of SAM's include, for example, bulk diffusion of SAM-forming molecules in the stamp, surface diffusion of the same along the stamp, surface diffusion of the same along the substrate, surface diffusion of the same along the SAM itself, interfacial transport of the same at the stamp-substrate interface, and reaction kinetics for the SAM-forming molecule with the substrate surface. The convolution of these kinetic factors makes the ability, let alone the sufficient optimization for commercialization, of microcontact printing to generate any particular pattern uncertain.
Another important challenge in microcontact printing relates to printing features of different scale simultaneously. Owing to the aforementioned (but not entirely understood) kinetic factors, it is unknown whether particular combinations of features sizes and spacings can be printed effectively and with useful speeds. No obvious and practical condition exists for printing alkanethiols to form both small and large features at the same time while maintaining the accuracy of the former.
Another important but unpredictable factor that influences whether a particular metal pattern can be successfully generated under a given set of printing and etching conditions is the surface onto which the SAM is printed, for example as determined by a substrate onto which the metal is deposited. Factors such as surface roughness and readily achievable cleanliness can vary substantially from one substrate type to the next (for example, polymer films as opposed to semiconductor wafers) and thus impacts the ability or conditions under which a metal pattern can be generated thereon.
Thus, there is a need in the art for combinations of pattern geometries and microcontact printing conditions, including ink formulation and stamp inking procedures, that allow for the effective and efficient etch-patterning of metal micropatterns, on commercially viable substrates for various applications.